[Lochlin]

To be a bit more specific, your cart has two clutches; the primary which is connected to the back of the engine and the secondary which is connected to the rear axle. The primary clutch should collapse when the cart is revving causing the belt to move towards the outer edge of that clutch. The secondary should expand when revving causing the belt to move towards the center of that clutch. Give those clutches a looksie and see if they are both operating right. It's been my experience that the primary clutches on these carts are pretty durable and don't fail much. The secondaries do.

Your compression is perfect so there are no concerns there. If the cart is running good on the flat then things with the engine should be ok. You are losing torque somewhere though. I would start with the clutches.